Search

The Mars Odyssey Gamma-Ray Spectrometer/Neutron Spectrometer/High Energy Neutron Detector has provided measurements of near-surface hydrogen, generally interpreted as resulting from water, in the equatorial and mid-latitudes. Water abundances as great as 10% by mass are inferred. Although such high abundances could be present as adsorbed water in clays or water of hydration of magnesium salts, other measurements suggest that this is not likely. The spatial pattern of where the water is located is not consistent with a dependence on composition, topography, present-day atmospheric water abundance, latitude, or thermophysical properties. The zonal distribution of water shows two maxima and two minima, which is very reminiscent of a distribution that is related to an atmospheric phenomenon. We suggest that the high water abundances could be due to transient ground ice that is present in the top meter of the surface. Ice would be stable at tens-of-centimeters depth at these latitudes if the atmospheric water abundance were more than about several times the present value, much as ice is stable poleward of about [+ or -] 60[degrees] latitude for current water abundances. Higher atmospheric water abundances could have resulted relatively recently, even with the present orbital elements, if the south-polar cap had lost its annual covering of C[O.sub.2] ice; this would have exposed an underlying water-ice cap that could supply water to the atmosphere during southern summer. If this hypothesis is correct, then (i) the low-latitude water ice is unstable today and is in the process of sublimating and diffusing back into the atmosphere, and (ii) the current configuration of perennial C[O.sub.2] ice being present on the south cap but not on the north cap might not be representative of the present epoch over the last, say, ten thousand years. Keywords: Mars; Neutrons; Mars Odyssey; Water ice; Mars climate

We produce bidirectional reflectance experimental measurements in the visible and near-infrared range of a macroscopic target simulating the case of a martian crater. Using Hapke's equation of radiative transfer, we compare the performance, in terms of mineralogical abundance determination, of different deconvolution processes on a multispectral image of the experimental target. In particular, we study the effects of the topography and the physical properties of natural rocky surfaces (e.g., local variations of incidence and emergence angles, grain size variations, mixtures of materials) on the data interpretation. For this purpose, we increase progressively the amount of quantitative knowledge available in terms of Hapke parameters description, textural properties and topography for the target. We estimate the accuracy of results in comparison with the known ground truth as a function of the level of knowledge we have of the target and carry out a critical assessment on the relative applicability of the different processes. This study shows that the more important parameters to take into account are (in decreasing order): (1) the textural roughness which is shown essential for the accurate determination of mineralogical abundances; (2) the disparity of Hapke parameters across the target (3) the topography (DEM) that has a limited influence on the results. These findings have obvious implications for interpreting planetary regolith reflectance properties in terms of photometry, spectroscopy and mineralogy, measured either from spaceborne (e.g., Io observations from Galileo, Mars from Mars-Express/HRSC and OMEGA) or in situ (Mars Pathfinder, MER) instruments. Keywords: Hapke's model; Experimental measurements; Photometry; Reflectance spectroscopy; Spectral mixing analysis; Planetary regolith

Using the Fourier Transform Spectrometer at the Canada-France-Hawaii Telescope, we observed a spectrum of Mars at the P-branch of the strongest C[H.sub.4] band at 3.3 [micro]m with resolving power of 180,000 for the apodized spectrum. Summing up the spectral intervals at the expected positions of the 15 strongest Doppler-shifted martian lines, we detected the absorption by martian methane at a 3.7 sigma level which is exactly centered in the summed spectrum. The observed C[H.sub.4] mixing ratio is 10 [+ or -] 3 ppb. Total photochemical loss of C[H.sub.4] in the martian atmosphere is equal to 2.2 x [10.sup.5] [cm.sup.-2] [s.sup.-1], the C[H.sub.4] lifetime is 340 years and methane should be uniformly mixed in the atmosphere. Heterogeneous loss of atmospheric methane is probably negligible, while the sink of C[H.sub.4] during its diffusion through the regolith may be significant. There are no processes of C[H.sub.4] formation in the atmosphere, so the photochemical loss must therefore be balanced by abiogenic and biogenic sources. Outgassing from Mars is weak, the latest volcanism is at least 10 million years old, and thermal emission imaging from the Mars Odyssey orbiter does not reveal any hot spots on Mars. Hydrothermal systems can hardly be warmer than the room temperature at which production of methane is very low in terrestrial waters. Therefore a significant production of hydrothermal and magmatic methane is not very likely on Mars. The calculated average production of C[H.sub.4] by cometary impacts is 2% of the methane loss. Production of methane by meteorites and interplanetary dust does not exceed 4% of the methane loss. Methane cannot originate from an extinct biosphere, as in the case of 'natural gas' on Earth, given the exceedingly low limits on organic matter set by the Viking landers and the dry recent history which has been extremely hostile to the macroscopic life needed to generate the gas. Therefore, methanogenesis by living subterranean organisms is a plausible explanation for this discovery. Our estimates of the biomass and its production using the measured C[H.sub.4] abundance show that the martian biota may be extremely scarce and Mars may be generally sterile except for some oases. Keywords: Mars, atmosphere; Exobiology; Atmospheres, composition; Spectroscopy; Infrared observations

This project examines the different approaches which deal with the theory of radiative transfer on atmosphereless bodies. We present the relative merits of two scattering theories based on the equivalent slab model: the extensively used Hapke theory (Hapke 1981, J. Geophys. Res. '86, 3039-3054) and the Shkuratov theory (Shkuratov et al. 1999, Icarus 141, 132-155). We found that their main difference is the role of the phase function of individual particles of regolith, which is predicted (and generally forward directed) in the case of the Shkuratov model instead of being a free parameter as formulated in the Hapke model. We also emphasize that different assumptions as to the manner in which different constituents are physically mixed in either model have a substantial effect on the synthetic spectra inferred. This leads to a significant extension of the validity of Hapke's or similar practical approaches to areas where these approaches are valid. We used two objects (the Centaurs 5145 Pholus and 8405 Asbolus) as examples. Previous modeling of the spectra of these two bodies with the Hapke approach gave suspect results in terms of the derived grain sizes, which were smaller than the wavelength, violating key assumptions of the model (Cruikshank et al. 1998, Icarus 135, 389-407 for Pholus; Barucci et al. 2000, Astron. Astrophys. 357, L53-56 for Asbolus). We considered several different types of powdered surfaces to interpret the surface composition of these two Centaurs. The effect of fine-scale contamination of water ice grains by small amounts of carbon and/or tholins is also explored. We can explain the strong red color and the rich near-infrared spectral signatures of Pholus using a five-component surface (contaminated water ice, amorphous carbon, Titan tholin, olivine, and methanol ice) where the grain sizes are consistent with the model assumptions. These components are similar to those inferred by Cruikshank et al. (1998), but we obtain very different grain sizes and relative abundances. For example, we obtain a relative abundance of water ice on the surface of Pholus of about 40% instead of 6% found with the Hapke model. Organic and carbonaceous components change by similar amounts. In the case of Asbolus, a tholin and amorphous carbon areal mixture can reproduce the spectrum, with water remaining at 9% or less. Using the albedo published by Fernandez et al. (2002, Astron. J. 123, 1050-1055) which is higher than most workers assume for Centaurs and Kuiper belt objects, a surface composition similar to that of Pholus is found. It appears that model-based uncertainties in relative compositions must be regarded with more attention. Key Words: radiative transfer; spectroscopy; centaurs.

Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros.

Spectrophotometric data for the 0.338- to 0.762-[[micro]meter] region on the main-belt M-asteroids 75 Eurydike and 201 Penelope at small phase angles have been obtained. The spectral observations of 201 Penelope were accompanied by photometric observations allowing an assessment of geometric albedo variation of Penelope with rotation. The reflectance spectra of the bodies are shown to have both similar and differing spectral features varying with rotation. The slightly red-sloped reflectance spectra may suggest the presence of an FeNi- or Fe-free component in the asteroid surface material. Common absorption bands in the spectra of Eurydike and Penelope can probably be attributed to pyroxenes (at 0.51 [[micro]meter]) and oxidized or aqueously altered mafic silicates (at 0.62 and 0.7 [[micro]meter]). A specific absorption feature of Penelope at 0.43 [[micro]meter] may be a result of electronic transitions in crystalline lattices of several different minerals present on the surface of the asteroid including some layer silicates. The presumed presence of phyllosilicates on the surface of 201 Penelope is explained as a result of the aqueous alteration of mafic silicates. Probable scenarios for the origin of the asteroids are also discussed. The conclusion is made that in spite of the asteroids' belonging to the M-class they have a considerable silicate component which manifests itself in some similar absorption features. Furthermore, a few of the main orbital elements of the bodies are very close. This permits the supposition that the bodies have a common origin.

The Eos family detected by Hirayama in 1918 has been always considered to be compositionally homogeneous. To investigate the composition and the homogeneity of the members of this family, we started a spectroscopic survey at the European Southern Observatory (ESO) with wavelength coverage ranging from 4800 to 9200 [Angstrom]. We observed 45 Eos asteroid members, which constitutes the first large survey of this family. Our results reveal the Eos objects have spectral signature characterizing the whole family: a maximum at [Lambda] [similar to] 8000-8500 [Angstrom] and a reflectivity gradient spanning a continuous range. Only two of the 45 investigated objects seem to be interlopers. While the lower range of this spectral distribution has been easily connected with CO-CV chondrites, we have found no satisfactory meteorite counterpart to the upper range. We have interpreted the spread out of Eos spectra to be the results of compositional variation among the Eos members, implying that the Eos parent body was partially differentiated. Moreover, a space weathering effect has been proven to be present, but with a minor role played in the diversity of Eos family, the major role being the compositional variation. Key Words: asteroids composition; spectroscopy; meteorites.

In this paper we report first optical reflectance spectra in the wavelength range 3800-9000 [Angstrom] for seven members of the Veritas asteroid family, as determined by V. Zappala, A. Cellino, P. Farinella, and A. Milani (1994, Astron. J. 116, 291-314). The observed asteroids are 490 Veritas, 844 Leontina, 1086 Nata, 2428 Kamenyar, 2934 Aristophanes, 5592 Oshima, and 1985 T[Q.sup.1]. In addition, we also observed the object 5107 1987 D[S.sub.6], which joins the Veritas family when a slightly more relaxed criterion of selection is adopted. The obtained spectra show a surprising slope gradient spanning from 0 to about 8%, a range that includes the slopes characteristics of all the low-albedo, primitive bodies (from C to D type). Taking into account the very compact structure of the family - the probability of finding interlopers inside the defined clustering is practically zero - this result seems to confirm the suggestion by F. Vilas and M. V. Sykes (1996, Icarus, in press) about the presence of thermally altered large asteroids inside the outer belt population; however, the hypothesis of possible space weathering processes cannot be completely ruled out. A tentative representation of the post-impact velocity field has been also obtained, showing a possible peculiar ejection of the fragments.

Spectra of 14 asteroids of varying classes were acquired using a moderate resolution spectrograph (dispersion 3.5 [Angstrom]/pixel) at the McDonald Observatory 2.7-m telescope as random targets of opportunity over the past 6 yr. The utility of high-quality measurements of asteroid reflectance in the 3200-5500 [Angstrom] wavelength range was demonstrated by the presence of subtle absorption features and the confirmation of the broad spectral properties of asteroids in this region. Notably, the sharp increase in reflectance with increasing wavelength for 5145 Pholus was confirmed, extending to the short wavelength of 3200 [Angstrom]. The NEAR target 253 Mathilde shows an absorption feature centered at 4300 [Angstrom] similar to features attributed to an [Fe.sup.3+] spin forbidden transition in the iron sulfate jarosite, a product of aqueoous alteration. Subtle absorption features near 4300 and 5065 [Angstrom] attributed to [Fe.sup.2+] spin-forbidden transitions in pyroxenes are apparent in the spectrum of 4 Vesta. Examples of the effects of signal loss due to differential refraction in the UV/blue, and the effects of slight misregistration of the sharper spectral features present in the solar spectrum at these wavelengths are presented and discussed.

Galileo SSI color data between 0.4 and 1.0 [[micro]meter] demonstrate that both Ida and Dactyl are S-type asteroids with similar, but distinct spectra. Small but definite color variations are also observed on Ida itself and involve both the blue part of the spectrum and the depth of the 1-[[micro]meter] pyroxene-olivine band. Ida's surface can be classified into two color terrains: Terrain A has a shallower 1-[[micro]meter] absorption and a steeper visible red slope than does Terrain B. Qualitatively, the color-albedo systematics of these two terrains follow those noted for color units on Gaspra and the variations in 1-[[micro]meter] band depth with weathering described by Gaffey et al. (Gaffey, M. J., J. F. Bell, R. H. Brown, T. H. Burbine, J. Piatek, K. L. Reed, and D. A. Chaky 1993. Icarus 106, 573-602). Terrain A, with its slightly lower albedo, its shallower 1-[[micro]meter] band, and its slightly steeper visible red slope relative to Terrain B could be interpreted as the 'more processed,' 'more mature,' or the 'more weathered' of the two terrains. Consistent with this interpretation is that Terrain A appears to be the ubiquitous background on most of Ida, while Terrain B is correlated with some small craters as well as with possible ejecta from the 10-km Azzurra impact structure. Because of these trends, it is less likely that differences between Terrains A and B are caused by an original compositional inhomogeneity within the body of Ida, although they do fall within the range known to occur within the Koronis family. The spectrum of Dactyl is similar to, but definitely different from, that of Terrain B on Ida. It does not conform to the pattern that obtains between the colors and albedos of Terrains A and B: the satellite's 1-[[micro]meter] band is deeper than that of Terrain B, but its albedo is lower, rather than higher. By itself, the deeper band depth could be interpreted, following Gaffey et al., to mean that Dactyl is a less weathered version of Terrain B on Ida, but such an interpretation is at odds with Dactyl's redder spectral slope. Thus, the explanation for the color difference between Dactyl and Ida is likely to be different from that which accounts for the differences between the two terrains on Ida. Given that Dactyl and Ida have very similar photometric properties (Helfenstein, P., J. Veverka, P. C. Thomas, D. P. Simonelli, K. Klassen, T. V. Johnson, F. Fanale, J. Granahan, A. S. McEwen, M. J. S. Belton, and C. R. Chapman 1996 Icarus 120, 48-65), thus ruling out any dramatic texture differences between the two surfaces, the most likely explanation is that the satellite has a slightly different composition (more pyroxene?) than Ida. The spectral difference is within the range reported by Binzel et al. (Binzel, R. P., S. Xu, and S. J. Bus 1993. Icarus 106, 608-611.) for members of the Koronis family, and could be caused by compositional inhomogeneities of the Koronis parent body rather than by post-breakup regolith processes.

Spatially resolved photometric observations of Phobos in nine narrow Band in the spectral range 315-600 nm were obtained by means of the KRFM instrument on board the Phobos spacecraft on 25 March 1989. There were initial difficulties with the interpretation of the data. However, some realistic solutions to these difficulties have been found, and now we present a revised version of the results that appears to be substantially free of the errors and uncertainties that affected previous publications. According to this version, the spectrum of Phobos (or at least of the parts of it observed by KRFM) is much redder than the spectra of carbonaceous chondrites. There are no direct spectral analogues between Phobos and any known examples of meteoritic materials or asteroids in the wide range from 200 to 3100 nm.

A pair of nonbrecciated basaltic lithologies connected along a planar igneous contact constitute a shergottite meteorite, EETA 79001 which is revealed by geochemical and petrological studies of the meteorite. The two lithologies, termed A and B, are basaltic types which rarely occur on the surfaces of planetary bodies. A Modified Gaussian Model (MGM) is used in the analysis of the reflectance spectrums of lithologies A and B. Application of MGM identifies the existence of two pyroxene phases in both lithologies. These two pyroxenes are responsible for all observed spectral features which were earlier attributed to plagioclase.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.forsciint.2008.12.018 Byline: Christoph Birngruber (a), Frank Ramsthaler (b), Marcel A. Verhoff (a) Keywords: Spectral imaging; Forensic hair examination; Hair color variation Abstract: Human hair is among the most common kind of evidence secured at crime scenes. Although DNA analysis through STR-typing is possible in principle, it is not very promising for telogenic hair or single hairs. For the mixed traces frequently found in practice, composed of different hair from an unknown number of individuals, mtDNA sequencing of each individual hair seems to be the only possible, even if technically elaborate, solution. If it were possible to pool all hair belonging to an individual prior to DNA analysis, then this effort could not only be reduced, but the number of hair for an STR-approach could also be increased. Although it is possible to examine hair microscopically, this method must be considered unsuitable for pooling, since the results depend strongly on examiner experience, and the hair cannot always be correctly attributed to an individual. The goal of this study was to develop an objective non-DNA-contaminative pooling method for hair. To this end, the efficacy of spectral imaging as a method of obtaining information -- beyond that obtained from a purely microscopic and morphological approach -- for the identification of individuals was investigated. Three hairs each from 25 test persons (female: 18; male: 7) were examined with a SpectraCube.sup.[R]-System and a light microscope. Six spectra were calculated for each hair, and the hairs from each individual were not only compared to each other, but also to those of the other individuals. From a forensic vantage, the examination showed, in particular, that individuals, whose hair could not be distinguished on the basis of morphology, could also not be accurately distinguished with the SpectraCube.sup.[R]. The intra-individual differences were, in part, greater than the inter-individual differences. Altogether, the study shows that a person's hair color, as perceived, is composed of many naturally different, individual colors. Author Affiliation: (a) Department of Legal Medicine, University of GieAen, Frankfurter StraAe 58, D-35392 GieAen, Germany (b) Department of Legal Medicine, University of Frankfurt/Main, Frankfurt/Main, Germany Article History: Received 23 September 2008; Revised 12 December 2008; Accepted 19 December 2008